Confocal microscopes optically section naturally or surgically exposed tissue to produce microscopic images of tissue sections. An example of a confocal microscope is the VivaScope® manufactured by Lucid, Inc. of Henrietta, N.Y. Other examples of confocal microscopes are described in U.S. Pat. Nos. 5,788,639, 5,880,880, and 5,995,867, and in articles by Milind Rajadhyaksha et al., “In vivo Confocal Scanning Laser Microscopy of Human Skin: Melanin provides strong contrast,” The Journal of Investigative Dermatology, Volume 104, No. 6, June 1995, and Milind Rajadhyaksha and James M. Zavislan, “Confocal laser microscope images tissue in vivo,” Laser Focus World, February 1997, pages 119-127.
Lucid's VivaScope®, and confocal imaging microscopes in general, use a raster scanned laser spot to illuminate the in-focus specimen plane. Refracted light from the in-focus plane is converted to an electrical signal, digitized using a conventional high-speed A/D (analog to digital) converter and displayed on a computer monitor as a two-dimensional image. The intensity of the image is both a function of imaging depth in a tissue specimen and the specimen's absorption characteristics. Typically, imaging depth is user controlled thereby requiring continuous laser power adjustment to maintain acceptable image brightness. Such manual control makes obtaining optimum imaging less efficient as numerous adjustment of laser power are often required as different sections of a tissue are imaged at different depths. Accordingly, it would be desirable to provide automatic control of laser power in a confocal microscope to maintain optimal image quality.
Although varying illuminating source intensity to maintain constant received signal strength is typically done in bar-code scanners, no mechanism has been provided for a confocal imaging system for controlling an illumination source, such as a laser, to improve the quality of two-dimensional confocal images.